lambda一些查询语句

<!--得分数据结构-->
1 <Score>
     <studentid>1</studentid>
     <courseid>1</courseid>
     <score>80</score>
   </Score>

<!--科目数据结构-->
1 <Course>
     <courseid>1</courseid>
     <name>攻击力</name>
   </Course>

<!--学生数据结构-->
1  <Student>
     <studentid>1</studentid>
     <name>大娃</name>
     <sex>男</sex>
     <age>13</age>
     <remark>力大无穷</remark>
   </Student>

 //按年龄排序
 public static List<Student> GetStudentsSortByAge()
         {
             try
             {
                //return Global.Data_students.OrderBy(stu => stu.age).ToList();
                 return  Global.Data_students.OrderByDescending(stu => stu.age).ToList();
             }
             catch (Exception exp)
             { }
             return null;
         }

 //指定年龄区间
 public static List<Student> GetStudentsByAgeBetween(int sage,int bage)
         {
             try
             {
                 return Global.Data_students.Where(stu => (stu.age >= sage && stu.age < bage)).ToList();
             }
             catch (Exception exp)
             { }
             return null;
         }

//姓名模糊查询
public static List<Student> GetStudentsByNameContains(string name)
        {
            try
            {
                return Global.Data_students.Where(stu =>stu.name.Contains(name)).ToList();
            }
            catch (Exception exp)
            { }
            return null;
        }

//指定性别查询
public static List<Student> GetStudentsBySexIs(string sex)
        {
            try
            {
                return Global.Data_students.Where(stu => stu.sex==sex).ToList();
            }
            catch (Exception exp)
            { }
            return null;
        } 

 //多表查询
 public static List<Result> GetScores()
         {
             try
             {
                 List<Result> lr = new List<WindowsFormsApplication1.Result>();
                 foreach (var v in Global.Data_scores.Join(Global.Data_courses, score => score.courseid, course => course.courseid, (score, course) => new
 8                 {
 9                     studentid = score.studentid,
10                     coursename = course.name,
11                     scores = score.score
12                 }).Join(Global.Data_students, score => score.studentid, student => student.studentid, (score, student) => new
13                 {
14                     studentname = student.name,
15                     coursename = score.coursename,
16                     scores = score.scores
17                 }).ToList()
                 )
                 {
                     Result r = new Result();
                     r.coursename = v.coursename;
                     r.score = v.scores;
                     r.studentname = v.studentname;
                     lr.Add(r);
                 };
                 return lr;
             }
             catch (Exception exp)
             { }
             return null;
         }